Automatic microcircuit bridge

This report summarizes the work done on the design, construction and test of an Offset Local Oscillator for use with the Tracking Servobridge Detector as part of a system for precision bridge-type measurements on quartz crystal resonators. The primary requirement for the Offset LO is to accept a generator input signal over the range of 0.8 to 220 MHz and produce an output which is offset from the input frequency by +80 kHz. This output serves as the local oscillator signal for a sensitive heterodyne detector and must be essentially free of a direct generator input component to avoid a spurious receiver response. The design approach used is to first produce a crude offset signal by phasing-type single-sideband techniques and then use a phase locked oscillator as an active filter to obtain the required spectral purity. The electronic circuits which implement this design are described in detail. The report contains the results of tests made on three Offset LO units. All requirements were met, and a viable design was achieved. The report also contains an analysis of an electronically tunable microcircuit RF bridge suitable for the automatic measurement of quartz crystal parameters. It is concluded that the measuring system studied indeed has the potential of making the desired measurements automatically. Possible sources of errors have been analyzed and corrective solutions proposed. Expected performance is in accordance with the latest guidelines for the system.